Different chargers are generally used to charge a first battery, which can also be regarded as a rechargeable battery. Typical chargers are supplied with a mains voltage, which means that their use is limited to a specific position or is at least associated with use together with plug sockets or fixed supply devices. Furthermore, chargers exist which charge batteries with current from solar cells. These are also portable. However, of course, they use light to operate. Furthermore, they are relatively cumbersome, because of the size of the solar cells.
Problems occur in charging the rechargeable batteries mentioned above in particular when using appliances which have short operating times with rechargeable batteries which times, for example, may be on the order of magnitude of a day, or in some cases more than this, or else in some circumstances considerably less than a day, depending, for example, on the age of the battery or the environmental conditions. In that case, a user is well-advised to carry a supply of charged batteries, which results in a certain amount of inconvenience. In addition, the batteries must be in transport packaging and, in particular, it must also be possible to distinguish between charged batteries and those which have already been discharged. This can lead to confusion, in many cases with a disturbing effect.
Typical appliances of this type are hearing aids. At the moment, these are generally operated by means of primary batteries, so-called “button cells.” This results in operating times on the order of magnitude of a few days, or even up to weeks. If the aim is to use rechargeable secondary batteries instead of button cells which can be used only once, for example, of the nickel/metal hydride type, then this results in the operating times mentioned above. It may therefore often be necessary to change or replace the battery during the day while away from home, as well, with the problems that a plurality of charged batteries must be carried as well, or else replacement batteries of sufficient capacity. If the operating time is more than one day, then the replacement problem will in some circumstances occur on the next day, that is to say likewise once again in the middle of the day. For this reason, hearing aids, for example, do not yet at the moment make use of the secondary batteries mentioned above of the nickel/metal hydride type.
It could be advantageous to provide a charger as well as a charging method which is portable and suitable for convenient use.